Self-cleaning paint coating and a method and agent for producing the same

ABSTRACT

A self-cleaning paint coating that exhibits the LOTUS EFFECT and an agent and a method for producing the same. The paint coating comprises a paint base coat and a topcoat. The topcoat includes structure-forming particles and is at least partially hydrophobic. The structure-forming particles have an average particle diameter of less than 100 nanometers (nm) and form elevations in the topcoat surface that are interspaced at a distance of less than 50 nm. The topcoat of the paint coating is formed from the agent. The agent contains a liquid medium, a hydrophobating agent dissolved in the liquid medium, and structure-forming particles suspended in the medium. The method of forming the paint coating comprises coating a substrate with the base coat, applying the topcoat agent to the partially cured or uncured base coat, and curing of the top coat, and if required, the base coat.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a National Stage application of PCT Application No.WO 02/064,266, filed Aug. 22, 2002, which claims priority to GermanApplication No. DE 101 06 213.3, filed Feb. 10, 2001, the disclosures ofwhich are hereby incorporated by reference in their entirety.

DESCRIPTION

The invention relates to self-cleaning lacquer coatings on any desiredsubstrates; the lacquer coatings display the Lotus Effect®. Theinvention also provides processes and compositions for the production ofthe self-cleaning lacquer coatings.

It is known that to achieve a good self-cleaning effect of a surfacethis must also have, in addition to a good hydrophobicity, a microroughsurface structure. The two features are realized in nature, for examplein the lotus leaf; the surface formed from a hydrophobic material haspyramid-shaped elevations a few μm from one another. Water dropssubstantially come into contact only with these peaks, so that thecontact area is tiny, which results in a very low adhesion. Theserelationships and the main usability of the “lotus effect” on industrialsurfaces are the doctrine of A. A. Abramzon, Khimia i Zhizu (1982), no.11, 38-40.

Without reference to the lotus effect, U.S. Pat. No. 3,354,022 discloseswater-repellent surfaces, wherein the surface has a microrough structurewith elevations and depressions and is formed from a hydrophobicmaterial, in particular a fluorine-containing polymer. According to oneembodiment, a surface with a self-cleaning effect can be applied toceramic tiles or to glass by coating the substrate with a suspensionwhich contains glass beads having a diameter in the range from 3 to 12μm and a fluorocarbon wax based on a fluoroalkyl ethoxymethacrylatepolymer. Disadvantages of such coatings are their lower resistance toabrasion and moderate self-cleaning effect.

The doctrine of EP Laid-Open Specification 0 909 747 A1 is a process forproducing a self-cleaning property on surfaces, in particular rooftiles. The surface has hydrophobic elevations with a height of 5 to 200μm. Such a surface is produced by application of a dispersion of powderparticles of an inert material in a siloxane solution and subsequentcuring. As in the process acknowledged above, the structure-formingparticles are not fixed to the surface of the substrate in anabrasion-stable manner.

The doctrine of EP Patent 0 772 514 is self-cleaning surfaces on objectswith a synthetic surface structure of elevations and depressions, thedistance between the elevations being in the range from 5 to 200 μm andthe height of the elevations being in the range from 5 to 100 μm, andthe structure comprising hydrophobic polymers or materials which havebeen rendered hydrophobic in a durable manner. Etching and embossingprocesses are suitable for formation of the structures, as well ascoating processes, such as gluing-on of a hydrophobic polymer. Ifnecessary, the structure formation is followed by a hydrophobization,for example a so-called silanization. The self-cleaning surfaces, thatis to say surfaces which are to be cleaned by gently agitated water,such as coatings of vehicles, should not be exposed to severemechanical, since the self-cleaning ability is thereby lost.

Similarly structured surfaces with hydrophobic properties are thedoctrine of EP 0 933 388 A2. The surface has elevations with an averageheight of 50 nm to 10 μm and an average distance of between 50 nm to 10μm, and a surface energy of the non-structured material of 10 to 20mN/m. To achieve a particularly low surface energy and thereforehydrophobic and oleophobic properties, the structured surface containsfluorine-containing polymers, or has been treated usingalkylfluorosilanes. Indications of also using coating processes forstructuring the surface instead of the shaping processes disclosed herecannot be found in this document.

The doctrine of DE Application 100 63 739.6 is substrates, such asglass, ceramic, plastic, metals and glazed or enamelled substrates, witha self-cleaning surface. The self-cleaning surface comprisesstructure-forming particles with an average diameter of less than 100nm, in particular less than 50 nm and at least 5 nm, and a layer-formingmaterial, this being an inorganic or organic material. Thestructure-forming particles are fixed to the substrate by means of thelayer-forming material. A portion of the primary particles and/oragglomerates thereof projects per se, or with a covering of thelayer-forming material, at least partly from the surface and in thismanner form elevations and depressions in the nanoscale range. Thestructured surface has a hydrophobic coating at least in part. Toproduce such self-cleaning surfaces, a composition which comprisesstructure-forming particles and an inorganic or organic layer-formingmaterial is applied to the substrate by means of known coatingprocesses, for example those of lacquering. After a cohesive and firmlyadhering layer has been formed by a heat treatment, a hydrophobizationfollows, for example using fluorine-containing silanes and/orfluorine-containing siloxanes. Although the process which is thedoctrine in this document can also be applied to substrates other thanthose mentioned therein, self-cleaning lacquer coatings which comprise abase lacquer layer and a top layer with an artificial surface structureare not mentioned. This document also contains no suggestion accordingto which the composition to be used for the production of aself-cleaning surface simultaneously comprises, apart from thestructure-forming particles and an inorganic or organic binder, ahydrophobizing agent. In the process which is the doctrine of thisdocument, the formation of the surface structure and thehydrophobization are carried out in separate steps.

The object of the present invention is accordingly to provide furthersubstrates with a self-cleaning surface. Another object is directed atproviding a composition with which the formation of a structured surfaceand the hydrophobization can be carried out simultaneously.

The objects mentioned and further objects such as are seen from thefollowing description of the invention are achieved by the self-cleaninglacquer coatings according to the invention, the compositions for theproduction thereof and the process.

A self-cleaning lacquer coating comprising a base lacquer layer and atop layer with an artificial surface structure, formed from particles,of elevations and depressions has been found, and is characterized inthat the particles have an average particle diameter of less than 100 nmand are at least partly bonded by means of a binder system in the toplayer, the average height of and the average distance between theelevations are less than 50 nm and the surface or top layer is at leastpartly hydrophobic.

The self-cleaning lacquer coating according to the invention has ananoscale surface structure with a hydrophobic character. Since thestructure-forming primary particles, which have an average diameter of<100 nm, in particular <50 nm to about 5 nm, can also form agglomeratesto a certain extent, the surface structure can also have asuper-structure with larger distances and heights, in addition to theabovementioned elevations and depressions. The average heights of anddistances between the elevations of the super-structure are in generalstill significantly below 1 μm.

The structured top layer can have been hydrophobized by a separatelyapplied hydrophobizing layer, which must be only a few atom layersthick, but according to a preferred embodiment of the invention thehydrophobizing agent is a constituent of the structure-formingparticles, and a top layer comprising a cured binder system.

The self-cleaning lacquer coatings according to the invention have anexceptionally good self-cleaning effect, which is also reflected in avery low roll-off angle of <3° C., and preferably <1° C. Since thedoctrine of EP Patent 0 772 514 is that the distance between theelevations of a self-cleaning surface structure should be in the rangefrom 5 to 200 μm and in EP Patent Application 0 933 388 an averageheight of and an average distance between the elevations of a structuredsurface are stated as 50 nm to 10 μm, it was not foreseeable that alacquer coating with a top layer with a considerably finer surfacestructure and a hydrophobic character has very good self-cleaningproperties. On the basis of the average diameter of thestructure-forming particles and the surface structure according to theinvention effected as a result, the lacquer coatings according to theinvention are also considerably more abrasion-resistant thanself-cleaning surfaces which comprise structure-forming particles with aconsiderably larger average diameter, for example >1 μm, bonded in abinder layer.

The structure-forming particles can be organic or inorganic substances.Among the inorganic substances there may be mentioned by way of example:metal oxides, mixed oxides, silicates, sulfates, phosphates, borates,metal sulfides, oxosulfides, selenides and sulfoselenides, metalnitrides and oxide-nitrides and metal powders. Among the organicstructure-forming particles there may be mentioned by way of examplecarbon blacks and nanoscale organic polymeric particles, and among thesefluorine-containing polymers. Structure-forming particles with theparticle diameter according to the claims, such as, in particular, about5 nm to less than 50 nm, are commercially obtainable. They can otherwisebe obtained by precipitation processes which are known per se or bypyrogenic processes, wherein gaseous starting substances are convertedinto pulverulent substances. The structure-forming particles areparticularly preferably naturally occurring, precipitated orpyrogenically prepared metal oxides from the series consisting of silica(SiO₂), titanium dioxide (TiO₂), aluminum oxide (Al₂O₃), zirconiumdioxide (ZrO₂) and tin dioxide (SnO₂). These oxides are particularlypreferably pyrogenically prepared oxides, and among these in particularsilica. Pyrogenic silicas are commercially obtainable with an averageprimary particle size in the range from about 5 to 40 nm.

The top layer of self-cleaning lacquer layers according to the inventioncomprises, in addition to the structure-forming particles, a curedbinder system, in particular an organic binder system. Thestructure-forming primary particles and agglomerates thereof are fixedin the binder system such that the surface structure is formed. Thebinder system can be a one- or multi-component system, and in addition ahydrophobizing agent contained in the top layer can be a constituent ofthe binder system. The latter is the case if both the binder system andthe hydrophobizing agent contain reactive groups which react with oneanother during curing.

According to one embodiment of the lacquer coating according to theinvention, the binder system of the base lacquer layer substantiallycorresponds to that of the top layer. As is shown, however, a reactivehydrophobizing agent can additionally have been incorporated into thelatter. According to an alternative embodiment, the binder systems ofthe base lacquer layer and of the top layer—independently of a reactivehydrophobizing agent optionally incorporated—differ chemically. If thebinder systems in the base lacquer layer and in the top layer aresubstantially the same, that part of the total coating in which thestructure-forming particles according to the invention are present isregarded as the top layer.

The weight ratio of the binder system to the structure-forming particlesbonded therein can be within wide limits; the ratio is determineddecisively by the form of application of the composition for theproduction of the top layer. The weight ratio is conventionally in therange from 1:50 to 10:1, but preferably in the range from 1:5 to 5:1. Itis essential that the structure-forming particles are present in asufficient amount so that during application and curing of the top layerthey do not sink into this completely, but form the nanoscale surfacestructure required according to the invention.

The structured top layer of the lacquer coating according to theinvention can have a hydrophobizing layer applied after the structureformation, but the hydrophobizing agents are preferably distributeduniformly within the top layer and are present in a concentration suchthat a sufficient surface hydrophobization results. Those hydrophobizingagents which have entered into chemical bonding with constituents of thebinder of the top layer and/or with reactive groups of thestructure-forming particles are preferably present. In addition oralternatively, an initially monomeric or oligomeric hydrophobizing agentcan also itself form a polymeric binder system during curing of the toplayer and fix the structure-forming particles on the base lacquer layer.

Both the base lacquer layer and the top layer can contain chemicallydifferent binder systems. Substantially all known lacquer systems arepossible for the base lacquer layer. These can be organic binders in anorganic, organic-aqueous or purely aqueous solvent system.Radiation-curing lacquer systems and powder coating systems can also beemployed. Examples of suitable binders are: cellulose-based binders,chlorinated rubber, polyvinyl compounds, acrylic and methacrylic resins,alkyd resins and other polyester resins, polymethane resins, epoxyresins, melamine, urea and phenolic resins and hydrocarbon resins.

According to a preferred embodiment, the base lacquer layer is based ona solvent-free or low-solvent binder system, for example one such as isused in powder coatings and radiation-curing lacquers. The binders forpowder coatings are, in particular, epoxy-polyester systems,polyester-triglycidyl isocyanurate systems, other epoxy resin systems,polyester-polyurethane systems and, to a lesser extent, alsothermoplastic resins, such as those based on polyethylene, polyamide,PVC, ethylene/vinyl alcohol copolymer and thermoplastic polyesters.Among the radiation-curing resin systems which are substantially basedon a combination of a prepolymer, a monomer and a photoinitiator theremay be mentioned by way of example acrylated epoxy resins, acrylatedurethanes and polyester acrylates; the monomers are, in particular,polyfunctional acrylic compounds, such as acrylic esters of polyhydricalcohols.

The usable self-cleaning lacquer coating according to the inventioncomprises the binder or binders contained in the base lacquer layer andtop layer in the cured state. The layer thickness of the top layer isconventionally considerably thinner than the layer thickness of the baselacquer layer. The layer thickness of the top layer is expediently inthe range of 1 to 10 times the average particle diameter of thestructure-forming particles.

The invention also provides compositions for the production of the toplayer of a preferred self-cleaning lacquer coating—this preferredlacquer coating comprises a hydrophobizing agent in uniform distributionwithin the top layer. The composition as a rule has a liquid to viscousconsistency and comprises as the main constituents a liquid medium, atleast one hydrophobizing agent suspended or emulsified, but preferablydissolved therein, and structure-forming particles with an averageparticle diameter of less than 100 nm, in particular less than 50 nm toabout 5 nm, optionally also to 1 nm, uniformly suspended therein. Thehydrophobizing agent can itself be the liquid medium or can be aconstituent thereof, but the hydrophobizing agent is preferablydissolved or emulsified/suspended in an organic or organic-aqueoussolvent system or in water.

The structure-forming particles contained in the composition are thosewhich have already been described above. They are preferably one or moremetal oxides from the series consisting of SiO₂, TiO₂, Al₂O₃, ZrO₂ andSnO₂.

In a preferred embodiment, the composition comprises structure-formingparticles and hydrophobizing agents in a weight ratio in the range from1:5 to 5:1. The concentration and the weight ratio of these constituentsin the composition according to the invention depend decisively on thedesired effect and the suitability of the hydrophobizing agent forrendering possible good hydrophobization of the surface when distributeduniformly within the top layer. Preferred compositions comprisestructure-forming particles, in particular oxides, in an amount of 0.1to 5 wt. % and hydrophobizing agent in an amount of 0.1 to 5 wt. %.

The composition expediently comprises one or more organic solvents whichare capable of dissolving the hydrophobizing agent or agents and thebinder or binders which may be present or precursors thereof. Suitablesolvents are, for example, monohydric alcohols having 1 to 4 C atoms andmono-, di- and trialkylene glycol monoalkyl ethers, wherein the alkylenegroup usually contains 2 or 3 C atoms and the alkyl group 1 to 4 Catoms.

If the composition according to the invention is binder-free, to obtaina scratch-resistant top layer which adheres firmly to the base lacquerlayer the solvent system of the composition must be chosen such thatthis comprises a solvent which is capable of partly dissolving thebinder system of the base lacquer layer so that the structure-formingparticles are fixed in regions of the base lacquer layer close to thesurface and can form the required structure. In this case, the choice ofsolvent depends both on the chemical nature of the binder system and onthe extent to which the base lacquer system is partly or completelycured by evaporation of solvents and/or by gelling. Binder-freecompositions which form the top layer are preferably applied to a baselacquer layer which has not yet dried, gelled or cured completely.

A preferred composition according to the invention for the production ofthe top layer additionally comprises one or more lacquer binders orprecursors thereof, in addition to the structure-forming particles, thehydrophobizing agent and conventionally one or more solvents. Theprecursors are compounds which are polymerizable and/or polycondensableand/or accessible to a polyaddition. If the lacquer binder is present inthe form of one or more precursors, the precursors are conventionally acombination of an oligomeric or polymeric compound and a second,optionally monomeric component which reacts with the oligomeric orpolymeric compound during the curing operation and forms the curedbinder. Such combinations of precursors of a lacquer binder can bepresent, for example, in radiation-curing lacquer systems and intwo-component powder coating systems. A composition comprising binderand/or precursors for the production of the top layer can comprise oneor more of the resin systems mentioned in the description of theself-cleaning lacquer coating. The expert will use those binders whichon the one hand ensure good fixing of the structure-forming particles,and on the other hand render possible a good adhesion to the baselacquer layer. The amount of lacquer binder or precursors employed inthe composition which forms the top layer can vary within wide limits.The composition expediently comprises one or more lacquer binders orprecursors thereof and structure-forming particles in a weight ratio inthe range from 1:50 to 10:1, in particular 1:5 to 5:1.

The hydrophobizing agents contained in the compositions according to theinvention can be known hydrophobizing agents, in particularfluorine-containing hydrophobizing agents. Preferred hydrophobizingagents are alkyl- and, in particular, fluoroalkylsilanes as well asoligomeric alkyl-, and in particular fluoroalkylsiloxanes, each of whichcontains one or more reactive groupings with which chemical bonds to thestructure-forming particles and/or constituents of the binder system ofthe top layer can be formed. The silanes or siloxanes preferably containone or more alkoxy groups, such as ethoxy groups, or acyloxy groups,such as acetoxy groups, as reactive groups. Such functional groups allowthe formation of a chemical bond to, for example, silanol groups ofstructure-forming silica particles, and also a bond to functional groupsof epoxy or polyester resins. At the same time, the hydrophobizing agentcan undergo self-polycondensation via these reactive groups. Silanizingagents which are particularly preferably to be used aretridecafluorooctyltriethoxysilane and oligomers thereof. Such productsare dissolved in the liquid medium of the composition according to theinvention or are themselves a constituent thereof.

The invention also provides a process for the production of theself-cleaning lacquer coating according to the invention. The processcomprises the following steps:

-   -   1. coating of a substrate with a coloured or non-coloured,        pigmented or non-pigmented coating composition which forms a        base lacquer layer by means of a known process appropriate for        the coating composition;    -   2. application of a liquid to paste-like composition which forms        a top layer to a cured, partly cured, gelled or non-cured base        lacquer layer by means of a conventional coating process        appropriate for the state of curing of the base lacquer layer,        the composition having the constitution described above;    -   3. curing of the top layer and, if necessary, the base lacquer        layer.

The conventional coating processes for the production of the baselacquer layer are, in the case where a pulverulent coating compositionis used, a powder coating process, for example electrostatic coating,fluidized bed coating or dry application by means of a doctor blade orthe like. If a liquid to paste-like lacquer is used to produce the baselacquer layer, coating processes such as brushing, dipping and sprayingcan be used. Since the composition which forms the top layer is ingeneral a liquid to paste-like composition, spraying and dippingprocesses are particularly suitable for the coating if the base lacquerlayer has not yet cured completely on application of the top layer. Ifthe base lacquer layer has already cured, other known lacqueringprocesses, such as brushing processes and known printing processes, canalso be used.

Before application of the top layer, the base lacquer layer isexpediently treated such that a largely closed layer has formed and, ifsolvents were contained in the coating material, a portion of thereadily volatile constituents has evaporated. If a pulverulent coatingcomposition is employed, a heat treatment accordingly follows the actualcoating process, during which the powder particles flow together and thebinder at least partly gels. If the composition which forms the toplayer does not contain its own binder but fixing of thestructure-forming particles takes place in the top region of the baselacquer layer, it is expedient to apply this composition before curingor in a state of curing/gelling of the binder system of the base lacquerlayer such that sufficient partial dissolving of the binder of the baselacquer layer by a solvent contained in the composition is renderedpossible, so that this binder also becomes the binder of the top layer.

According to a particularly preferred embodiment, a composition whichforms the top layer and comprises the following main components isapplied: 0.1 to 5 wt. % of structure-forming particles, in particularparticles with an average particle diameter of less than 50 nm and atleast about 5 nm; 0.1 to 5 wt. % of hydrophobizing agent, in particularfrom the series consisting of fluorine-containing alkoxysilanes andalkoxysiloxanes; 80 to 99.7 wt. % of liquid medium based on water and/orone or more organic solvents, in particular alcoholic solvents. Ifnecessary, conventional processing auxiliaries, such as suspensionauxiliaries and flow auxiliaries, in the conventional low concentrationcan additionally be present to a small extent.

The curing of the top layer and, if the base lacquer layer has not yetcured, also of the base lacquer layer is preferably carried out by aheat treatment. This is expediently carried out at not less than 100°C., in particular 150 to 280° C. During the curing, chemical reaction ofreactive groups of the hydrophobizing agent with reactive groups of thebinder and/or of the structure-forming particles also takes place.

The advantages of the invention lie in the fact that lacquer coatingswhich chemically are very different can be converted into a goodself-cleaning lacquer coating. The coatings have a high scratchresistance and can therefore also be used in those fields of use inwhich mechanical stresses cannot be ruled out completely. Thecompositions according to the invention can be prepared in a simplemanner and applied like any other liquid lacquer.

The following examples illustrate the invention.

EXAMPLES

An aluminum sheet (9×6 cm, 4 mm thick) was coated with a powder coatingbased on a polyester-epoxy resin by dry application by means of a slide.The dry layer thickness was 300 μm. The base lacquer layer was gelled orcured under the conditions (° C./duration) stated in the table(conditioning).

The constitution (data in g) of the composition which forms the toplayer follows from the table. Pyrogenic silica (Aerosil® from Sivento)was employed as the structure-forming particles, and an alcoholicsolution of tridecafluorooctyltriethoxysilane (Sylan® F8262 or F8263from Sivento) was employed as the hydrophobizing agent. The constituentswere made into a paste by means of a triple roll mill. The compositionwas applied as stated in the table. The amount applied was in each caseabout 0.25 g/sheet. Drying and curing were carried out for 20 minutes at200° C.

The lacquer coatings proved to be scratch-resistant and had a goodself-cleaning effect—roll-off angle less than 3°, in particular lessthan 1°.

TABLE Example no. 1 2 3 4 5 6 7 Conditioning ° C. 140 140 140 140 140140 140 Min 12 16 10 10 12 10 10 Composition Aerosil 200¹⁾ 0.25 2 2 1 11 Aerosil 380²⁾ 1 Sylan F8262³⁾ 6 Sylan F8263⁴⁾ 48 48 40 40 45 45Ethanol 10 10 PGMME⁵⁾ 0.4 3.2 3.2 Medium⁶⁾ 10 10 5 5 Application ScreenBrush Spray Spray Spray Spray Spray printing gun gun gun gun gunRoll-off angle 3° <3° 2° <2° <2° <1° <1° ¹⁾ and ²⁾Primary particles d =12 nm and 7 nm respectively ³⁾ and ⁴⁾1% solution of the silane inalcohols ⁵⁾PGMME: Propylene glycol monomethyl ether ⁶⁾Medium from dmc²Degussa Metals Catalysts Cerdec AG contains hydroxypropylcellulose(approx. 10%) as the binder in an alcoholic solvent mixture.

1. A self-cleaning lacquer coating, comprising: a base lacquer layer;and a top layer comprising particles and a first binder systemoverlaying the base lacquer layer, wherein the binder system binds theparticles such that the top layer has a structured surface of elevationsand depressions formed by the particles, wherein the particles have anaverage particle diameter of less than 100 nanometers, wherein theaverage height of, and the average distance between, the elevations areless than 50 nanometers wherein the surface or top layer is at leastpartly hydrophobic, and wherein the weight ratio of binder system toparticles is from about 1:50 to about 10:1.
 2. The self-cleaning lacquercoating of claim 1, wherein the structure-forming particles have anaverage diameter of at least 5 nanometers to less than 50 nanometers. 3.The self-cleaning lacquer coating of claim 1, wherein the particlescomprise a material selected from the group consisting of metal oxides,mixed oxides, silicates, sulfates, phosphates, borates, carbon blacks,metal powders, metal sulfides, selenides, sulfoselenides, oxosulfides,metal nitrides, oxide-nitrides, organic polymers, and pigments, andcombinations thereof.
 4. The self-cleaning lacquer coating of claim 3,wherein the particles are metal oxides from the group consisting ofSiO₂, TiO₂, Al₂O₃, ZrO₂ and SnO₂, and combinations thereof.
 5. Theself-cleaning lacquer coating of claim 1, wherein the base lacquer layercomprises a second binder system, wherein the second binder system isthe same as the first.
 6. The self-cleaning lacquer coating of claim 1,wherein the binder system comprises constituents and the particlescomprise reactive groups, and an in-situ polymerized fluorine-containinghydrophobizing agent, wherein the hydrophobizing agent is bonded to atleast one of the constituents and the reactive groups, therebyhydrophobizing at least a portion of the surface of the top layer. 7.The self-cleaning lacquer coating according to claim 1, wherein thebinder system is formed from a resin selected from the group consistingof epoxy resins, polyester resins, polymethane resins, cellulose-basedresins and vinyl resins.
 8. A self-cleaning lacquer coating, comprising:a base lacquer layer; and a top layer comprising particles and a bindersystem overlaying the base lacquer layer, wherein the binder systembinds the particles such that the top layer has a structured surface ofelevations and depressions formed by the particles, wherein theparticles have an average particle diameter of less than 100 nanometers,wherein the average height of, and the average distance between, theelevations are less than 50 nanometers and the surface or top layer isat least partly hydrophobic, and wherein the binder system and theparticles are present in the top layer in a weight ratio of bindersystem to particles in the range of from about 1:5 to about 5:1.
 9. Acoating, comprising: a first layer comprising a polymeric resin; and asecond layer overlaying the first layer and having an outer surface,wherein the second layer comprises: a binder; a plurality of particleshaving an average diameter from about 7 nanometers to about 12nanometers; and a multifunctional halogenated silane or siloxanematerial; wherein the weight ratio of binder to particles is from about1:50 to about 10:1; the outer surface having depressions and elevationsthat extend relative to the outer surface, the depressions andelevations being formed by the presence or absence in the outer surfaceof the plurality of particles, the average height of, and the averagedistance between, the elevations being less than 50 nanometers, and themultifunctional halogenated material being bound to the outer surface ofthe second layer through the multifunctional group and being orientedrelative to the outer surface such that a halogen group on the silane orsiloxane material can hydrophobize the outer surface, thereby reducingthe roll-off angle relative to the outer surface to be less than about 3degrees.
 10. The coating according to claim 9, wherein: the polymericresin is selected from the group consisting of polyester-epoxy,polyester isocyanurate, polyester polyurethane, and epoxy; the binder isselected from the group consisting of hydroxypropyl cellulose,chlorinated rubber, polyvinyl, acrylic, alkyd, melamine, phenolic, andpolyester; the plurality of particles comprise precipitated silica; themultifunctional halogenated material is trifluorooctyltriethoxysilane oran oligomer thereof and the roll-off angle relative to the outer surfaceis less than about 1 degree.
 11. A process for producing a self-cleaninglacquer coating, comprising: coating a substrate with a coatingcomposition having a consistency of a liquid or of a paste so as to forma base lacquer layer; determining a state of cure of the base lacquer asbeing cured, gelled, partly cured or non-cured; selecting a coatingprocess for coating the base lacquer layer with regard to the state ofcure of the base lacquer layer; coating the base lacquer layer with aliquid medium comprising: a hydrophobizing agent being dissolved in theliquid medium, and structure-forming particles being suspended generallyuniformly in the liquid medium, the particles having an average particlediameter of less than about 100 nanometers, and a binder system operableto bind the particles to form a surface of a top layer wherein thesurface is structured with elevations and depressions that extendrelative to the top layer surface, and thereby to form the top layeroverlaying at least a portion of the base lacquer layer; wherein theaverage height of, and the average distance between, the elevations areless than 50 nanometers, wherein the weight ratio of binder system toparticles is from about 1:50 to about 10:1, and wherein the surface ortop layer is at least partly hydrophobic; and curing the top layer, andif the base lacquer layer is gelled, partly cured or non-cured alsocuring the base lacquer layer.
 12. The process of claim 11, furthercomprising at least partially evaporating solvents contained in thecoating composition to effect at least partial gelling, at least partialdrying, or at least partial curing of the base lacquer layer prior toapplying the liquid medium to the base lacquer layer.
 13. The processaccording to claim 11, further comprising heat treating the top layer ata temperature in a range of from about 100 degrees Celsius to about 250degrees Celsius subsequent to the step of applying the liquid mediumwhich forms the top layer to the base lacquer layer.
 14. The processaccording to claim 13, wherein the heat treating temperature is in arange of from about 150 degrees Celsius to about 250 degrees Celsius.15. A process for producing a self-cleaning lacquer coating, comprising:coating a substrate with a coating composition having a consistency of aliquid or of a paste so as to form a base lacquer layer, determining astate of cure of the base lacquer as being cured, gelled, partly curedor non-cured; selecting a coating process for coating the base lacquerlayer with regard to the state of cure of the base lacquer layer;forming a top layer, by combining: 0.1 to 5 wt. % of structure-formingoxide particles having an average particle diameter of about 5 to about50 nm; 0.1 to 10 wt. % of layer-forming binders or precursors; 0.1 to 5wt. % of hydrophobizing agents selected from the group consisting offluorine-containing alkoxysilanes and fluorine-containingalkoxysiloxanes; and 80 to 99.7 wt, % of a solvent selected from thegroup consisting of water, organic solvents, and combinations thereof;coating the base lacquer layer with a liquid medium comprising: ahydrophobizing agent being dissolved in the liquid medium, andstructure-forming particles being suspended generally uniformly in theliquid medium, the particles having an average particle diameter of lessthan about 100 nanometers, and a binder system operable to bind theparticles such that a surface of the top layer is structured withelevations and depressions that extend relative to the top layersurface, wherein the top layer overlays at least a portion of the baselacquer layer; and curing the top layer, and if the base lacquer layeris gelled, partly cured or non-cured also curing the base lacquer layer.16. A process for producing a self-cleaning lacquer coating, comprising:coating a substrate with a coating composition having a consistency of aliquid or of a paste so as to form a base lacquer layer, determining astate of cure of the base lacquer as being cured, gelled, partly curedor non-cured; selecting a coating process for coating the base lacquerlayer with regard to the state of cure of the base lacquer layer;coating the base lacquer layer with a liquid medium to form a top layer,the top layer comprising particles and a binder system, the liquidmedium comprising a solvent, a hydrophobizing agent, andstructure-forming particles, wherein the weight ratio of binder systemto particles is from about 1:50 to about 10:1; the hydrophobizing agentand the particles being dissolved or suspended in the solvent, theparticles having an average particle diameter of less than about 100nanometers, the solvent being operable to dissolve at least a surfaceportion of the base lacquer layer and cause at least a portion of thedissolved binder to migrate from the base lacquer layer into the toplayer so that the top layer comprises a predetermined amount of migratedbinder sufficient to bind the particles upon curing; and curing the baselacquer layer and the top layer such that a surface of the top layer isstructured with elevations and depressions that extend outward relativeto the surface of the top layer, said elevations and depressions beingformed by the particles, the average height of, and the average distancebetween the elevations being less than 50 nanometers, and the surface ofthe top layer being at least partially hydrophobic.